This invention relates to a breather provided in a power-transmission casing for use in a motorcycle.
As is well known, a power-transmission casing is mounted to a body of a motorcycle in parallelism thereto. The casing is extended at a position between an engine and a rear wheel in order to cover a gear transmission mechanism coupled to the rear wheel and a power transmission means such as V-belt trained over an engine output shaft and the gear transmission mechanism. According to a conventional power transmission casing, a breather passage is integrally formed at an outer peripheral portion thereof so as to provide gas communication between inside and outside of the casing. The breather passage has one outer end formed with a breather hole opened to an atmosphere. Therefore, there has been drawbacks in that water may enter the casing through the breather passage. For example, in washing or cleaning of the motorcycle, if water is present at the breather hole, the water may be drawn into the casing due to the negative pressure created in the casing. The negative pressure is generated due to the immediate cooling of the casing in washing the same with water. Such sucked water is mixed with oil accumulated in the casing for lubrication of gear-transmission mechanism, thereby degrading the lubricating of the oil
Further, there has been demanded to commonly use the breather passage for gas communication of the two power transmission casings, one being the casing for gear-transmission mechanism, and the other being the casing for power transmission means.
In another type of the breather system, only single breather hole is formed at the bottom portion of the casing extending in the vertical direction. In such case, when the motorcycle runs through a puddle or stream, water may enter the casing and contact the power transmission means.